This invention pertains to a shaft coupling system for coupling a shaft, typically a graphite shaft, to an outer sleeve or outer surface. This invention is particularly useful in a molten metal environment.
Molten metal may be one of the more difficult environments in which to maintain rotating and other equipment due to the heat and the corrosive factors within the molten metal. The submerged components of this equipment is typically made of graphite or similar materials due to the ability of these types of material compositions to withstand the heat and corrosive effects of the molten metal. While graphite and other similar materials withstand the molten metal well, they are susceptible to oxidation.
In order to utilize graphite and obtain its benefits in the molten metal in situations where oxygen is present above or around the molten metal, outer surfaces and/or outer sleeves are placed around the graphite where it may or will encounter oxygen. In shaft applications using graphite, typically an outer sleeve or outer surface of silicon carbide or of a ceramic will be used to completely surround and protect the graphite.
It should be noted and will be recognized by those of ordinary skill in the art that while references may be made herein to the molten aluminum environment, this is only used to give an example and not to limit the invention thereto since the system disclosed herein may be used in numerous other applications, including all molten metal applications, as well as in any other shaft coupling applications.
The outer sleeve or surface must somehow be fixed to the graphite shaft or other component being protected. In the typical situation, this is accomplished by manufacturing the outer sleeve or outer surface with an inner diameter which corresponds closely to the outer diameter of the shaft on which it will be attached. To install or attach the sleeve to the shaft, the shaft is typically covered with cement and the sleeve is then slid over the shaft. Then, when the cement dries, there is a solid attachment or coupling of the shaft to the outer sleeve/surface.
If air gaps are present between the shaft and the sleeve, the air gaps tend to cause cracks in the sleeves/outer surfaces. The air gaps cause graphite deterioration through oxidation, and ultimately leads to the failure of the shaft as oxidation is allowed to attack the graphite. The shaft must then be replaced.
Air gaps typically occur when the sleeve or outer surface is initially installed because as the sleeve is placed over the shaft (which is covered with cement), the sleeve tends to displace cement from some areas on the shaft despite the installers best efforts to avoid this situation.
The replacement or servicing of a shaft operating submersed in molten metal is a time consuming and expensive task. First, the shaft must be removed from the molten metal, thereby causing down time of the metal furnace if that is the operating environment. Then the shaft and other equipment must be allowed to sufficiently cool to allow it to be disassembled. Once the deteriorated components of a typical shaft are sufficiently cool, the molten metal built up on the various pump surfaces must be sufficiently removed to allow disassembly and/or re-use of the pump components. Then the pump must be reassembled with the combination of old components or parts, along with the replacement parts. The cost of downtime of a molten metal production line is very expensive and in addition to the actual repair costs.
It is therefore an object of this invention to provide an alternative way to couple, attach or secure the shaft to the outer sleeve or outer surface.